UPD: According to Sky News, the number of people killed in the terrorist attack are 4.

UPD: In two terrorist attacks in London, two people were killed while several others injured. Police have confirmed that the incident is a terrorist incident.

A man wielding a knife was shot by police close to the Houses of Parliament in central London, while two other persons were killed in an incident on Westminster Bridge when a vehicle mowed down pedestrians. Police says the suspect first drove into pedestrians on Westminster Bridge, killintg two people with a black SUV-like Hyundai i40, before attacking the police officer outside parliament.
Politicians and journalists have tweeted about hearing loud crashes outside the buildings,
Witnesses said they saw people being treated for wounds and reported seeing a man with a knife in the grounds.
Staff inside Parliament were told to stay inside their offices. The BBC’s Laura Kuenssberg said police told her someone had been shot.
She said MPs had told her they heard “three or four gunshots”.
Tom Peck, political editor for the Independent, tweeted: “There was a loud bang. Screams. Commotion. Then the sound of gunshots. Armed police everywhere.”
Scotland Yard said it was called to a firearms incident on Westminster Bridge amid reports of several people injured.
Transport for London said Westminster underground station has been shut at the police’s request. According to Commons leader David Lidington, a police officer has been stabbed in the Houses of Parliament in central London.

Meanwhile,  reports speak of 12 pedestrians being injured by a car at Westminster Bridge. Eyewitnesses say at least 12 people were injured on Westminster Bridge, while a Ferry appears to have crashed into it and another vehicle appears to have crashed into a fence outside the Parliament.

source: bbc.com